The measurement of a load of a vehicle is performed mainly on a large vehicle such as a truck and, for example, for the purposes of preventing traffic accidents such as turnover due to overload, and of preventing deterioration of vehicles and road surfaces from being stimulated.
Conventionally, a load of a vehicle is measured by placing a vehicle to be measured on a platform weighing machine which is so called "KANKAN" in Japanese. The facilities are large scaled, and necessitate a wide installation space, so that the number of platform weighing machines which can be installed is limited. Therefore, a number of vehicles cannot be measured at a time. Additionally, the installation cost is increased.
In recent years, a load measuring apparatus which is mounted on a vehicle itself to measure a load is provided.
In a conventional load measuring apparatus which is mounted on a vehicle, generally, sensing devices for measuring a load, for example, strain gauge sensors are attached to arcuate leaf springs which are interposed between a rear body frame and axle shafts, and the load is calculated based on the total of measured values of the sensing devices.
Hereinafter, the structure of a conventional load measuring apparatus which was proposed by the applicant will be described with reference to FIGS. 8 and 9.
FIG. 8 is an exploded perspective view of a large vehicle such as a truck and showing a vehicle portion in which the load measuring is performed by the load measuring apparatus. In the figure, 31 designates a leaf spring which functions as a suspension, and 32 designates a rear body frame.
Two yoke brackets 33 are fixed to the rear body frame 32 with being separated from each other in the longitudinal direction by a distance corresponding to the size of the leaf spring 31. One end of the leaf spring 31 is swingably coupled to one of the brackets 33 via a cylindrical pin 33A.
A yoke shackle 34 is swingably coupled to the other bracket 33 via a cylindrical shackle pin 3. The other end of the leaf spring 31 is swingably coupled to the shackle pin 34 via a cylindrical pin 34A. As a result, the leaf spring 31 is attached to the rear body frame 32. An axle shaft (not shown) is attached to the rear body frame 32 via the leaf spring 31.
FIG. 9(a) is a section view of the shackle pin 3 and showing a location of a sensing device in the load measuring apparatus proposed by the applicant, and FIG. 9(b) is a view looking in the direction of the arrow A of FIG. 9(a).
As shown in FIG. 9(a), an insertion hole 33b for the shackle pin 3 is formed on each of side faces 33a of the yoke bracket 33. On one side face 33a, as shown in FIG. 9(b), a slit 33c which elongates from an end of the side face to the insertion hole 33b is formed.
In addition, as shown in FIG. 9(a), a through hole 33d which elongates in a direction perpendicular to the insertion hole 33b and passes through the portions of the side face 33a on both sides of the slit 33c is formed in the one side face 33a.
The through hole 33d is configured in such a manner that, in a condition where a fixing bolt 16 for the shackle pin 3 is inserted as shown in FIG. 9(b), the fixing bolt 16 can be engaged with an annular groove 3a formed on the surface in the vicinity of an end portion of the shackle pin 3 as shown in FIG. 9(a).
An insertion hole 34a having an inner diameter corresponding to the insertion hole 33b is formed in a basal portion of the shackle 34.
The shackle 34 is attached to the bracket 33 in the following manner.
First, the shackle pin 3 is inserted into the insertion holes 33b, 34a, and 33b of the side faces 33a of the bracket 33 and the shackle 34 which are mutually positioned. The fixing bolt 16 is inserted into the through hole 33d, so as to be engaged with the groove 3a of the shackle pin 3.
Next, the gap of the slit 33c is reduced by screw motion of a nut 16A which is screwed onto an end of the fixing bolt 16 as shown in FIG. 9(b).
This causes the inner diameter of the insertion hole 33b of the one side face 33a to be reduced, thereby clamping and fixing the shackle pin 3.
In this way, the attachment is completed.
Then, as shown in FIG. 9(a), the sensing device 2 for measuring a load is fitted into a hollow hole 3b which is bored in a center portion of one end of the shackle pin 3 in the axial direction, and a screw groove 3c is provided in the vicinity of an entrance of the hole 3b.
The sensing device 2 is made of a magnetic material such as Permalloy and comprises a center plate-like member 2e and cylindrical fixing members (holders) 2d which are on both sides of the center plate-like member. A resistance wire 2a serving as a sensing portion is attached by an adhesive to a portion of the plate-like member 2e. A lead wire 2c from the resistance wire 2a is led through the hole 3b of the shackle pin 3 to the outside from the hole 3b.
A mudguard tap 17 is screwed to the entrance of the hole 3b by means of the screw groove 3c. The lead wire 2c is led through a hole formed in a center portion of the tap 17 to the outside of the hole 3b. A hole 3d formed on the side opposite to the hole 3b of the shackle pin 3 is a hole for supplying grease.
The sensing device 2 of the above-described conventional load measuring apparatus is positioned in a location which is in the hole 3b of the shackle pin 3 and stretches over the shackle 34 and the one side face 33a of the bracket 33. When a load F is imposed on the shackle pin 3 from the vehicle via the rear body frame 32 and the brackets 33, a shearing force acts on the shackle pin 3, so that the sensing device disposed in the inside is distorted. This causes the sensing output to be varied and the load of the vehicle is detected.
The sensing device 2 must be fixed inside the hole 3b so that the direction of the plate-like member 2e coincides with the load direction to the shackle pin 3.
In the conventional art, therefore, a method in which an adhesive is applied to the surface of the sensing device 2 and the sensing device 2 is then fitted into the hole 3b of the shackle pin 3, and another method in which the sensing device 2 in the hole 3b is irradiated with a beam through a small hole elongating from the outer circumference of the shackle pin 3 to the hole 3b, and the sensing device 2 is welded to the inner wall of the hole 3b are mainly used.
However, the fixing by using an adhesive involves a problem in the strength of adhesive bonding, and the fixing by the beam welding necessitates troublesome processes such as that a small hole is bored in the shackle pin 3, and that the optical axis of the beam is precisely aligned with the small hole.
To comply with this, the applicant has proposed a sensing device and a method of fixing the sensing device which can solve the problems, in Unexamined Japanese Patent Publication No. Hei. 6-313740.
FIG. 10 is a perspective view of the proposed sensing device. The sensing device 22 comprises a center plate-like member 22e and fixing members 22da and 22db on both sides thereof, in a similar manner to the above-described conventional sensing device 2.
In the sensing device 22, the one fixing member 22da is formed so as to have a substantially truncated cone shape of a tapered form. In the other fixing member 22db, a groove 22dc for leading out a lead wire of a resistance wire which is not shown in the figure, from the center plate-like member 22e, and a key groove 22dd into which a wedge key 4 (FIG. 11) is pressingly fitted are formed.
In order to internally house and fix the thus configured sensing device 22, a hole 3b of a shackle pin 3 is structured so that the inner diameter of a portion of the hole 3b near the entrance is different from that of a portion of the hole 3b on the innermost side as shown in a section view of FIG. 11. Specifically, a portion of the hole 3b which faces the one fixing member 22da in a condition where the sensing device 22 is housed is formed as a tapered face 3ba corresponding to the outer diameter of the fixing member 22da.
The sensing device 22 is inserted from the side of the one fixing member 22da into the hole 3b. When the outer circumference of the fixing member 22da comes in contact with the tapered face 3ba and the sensing device 22 is stopped at the depth of the hole 3b, the wedge key 4 is pressingly fitted into a gap between the key groove 22dd and the inner circumference of the hole 3b, whereby the sensing device 22 is fixed in the insertion direction and a circumferential direction of the hole 3b. Finally, a tap 17 is screwed to the screw groove 3c at the entrance of the hole 3b, so as into close the hole 3b.
In the measurement of a load F of a vehicle by using the sensing devices 2 and 22 in the shackle pin 3 shown in FIGS. 9 to 11, the brackets 33 are integrally fixed to the rear body frame 32. If the remaining brackets 33 and the shackle 34 are integrated, therefore, all the components in the range from the rear body frame 32 to the shackle 34 are integrated.
Accordingly, a detection value according to the actual load can be obtained from the outputs of the sensing devices 2 and 22 irrespective of the position in the axial direction of the shackle pin 3 where the load center acting on the shackle pin 3 is located, that is, without being affected by conditions such as the loading condition of baggage on the rear body, the inclination condition of the road, and the steering condition of the handwheel.
Actually, however, the inner diameters of the insertion holes 33b, 34a, and 33b of the side faces 33a of the bracket 33 and the shackle 34 are larger than the outer diameter of the shackle pin 3 in order to facilitate the insertion of the shackle pin 3 into the insertion holes 33b, 34a, and 33b. As shown also in FIG. 9(a), a slight clearance is formed between them, so that the bracket 33 and the shackle 34 are not integrated via the shackle pin 3.
Accordingly, for example, in a condition where the load is equally dispersed in the right and left directions of the vehicle, as schematically shown in FIG. 12(a), the load center W acting on the shackle pin 3 is located in a substantial center position in the axial direction of the shackle pin 3, and halves of the load F are equally imposed from both the side faces 33a of the bracket 33 on both the ends of the shackle pin 3 in the axial direction, respectively. Thus, the load can be correctly obtained by doubling the output of the sensing device 2, or by other methods. In such a condition, therefore, there arises no problem.
As schematically shown in FIG. 12(b), if the load dispersion of the vehicle is displaced in either of the right and left directions, however, the load center W is displaced toward one end side of the axial direction of the shackle pin 3. For example, 3/4 of the load F is imposed from one side face 33a of the bracket 33 on one end side of the axial direction of the shackle pin 3, and 1/4 of the load F is imposed from the other side face 33a of the bracket 33 on the other end side of the shackle pin 3. Thus, the imposition of the load on the ends of the shackle pin 3 is unbalanced. This causes a disadvantage in that the load cannot be correctly calculated from the output of the sensing device 2.
Additionally, it is necessary to form the one fixing member 22da of the sensing device 22 and the tapered face 3ba of the shackle pin 3 shown in FIGS. 10 and 11 so as to have a tapered shape. Furthermore, there is a disadvantage in that, in order to surely fix the sensing device 22, both of the one fixing member 22da and the tapered face 3ba should be machined with high precision.
According to the above-described fixing method, the sensing device 22 is pressingly fitted into the hole 3b and pressed against the innermost side by applying a force to some extent so that the outer circumference of the one fixing member 22da is closely in contact with the tapered face 3ba. During this process and a process of pressingly fitting the wedge key 4 into the gap between the key groove 22dd and the inner circumference of the hole 3b, it is necessary to control the application of the force so as to realize an appropriate condition. This produces a disadvantage in that the assembling process is complicated, and hence the production cost is increased.
The invention has been conducted in view of the above-described circumstances. It is a first object of the invention to provide, in a load measuring apparatus which measures a vehicle load by using sensing devices for an axle member in which the vehicle load is dispersedly imposed on both ends, a structure for mounting sensing devices for measuring a vehicle load which allows the sensing devices to obtain a detection value according to the actual load without being affected by the loading condition of baggage on the rear body, the inclination condition of the road, the steering condition of a handwheel, and the like.
It is a second object of the invention to provide a structure for mounting sensing devices for measuring a vehicle load which can simplify a process of attaching the sensing device to the axle member and reduce the production cost.